type of reaction have been created, including the Lotka-Volterra model, the Brusselator and the Oregonator. The latter was designed to simulate the Belousov-Zhabotinsky reaction. Types Belousov–Zhabotinsky (BZ) reaction A Belousov–Zhabotinsky reaction is one of several oscillating chemical systems, whose common element is the inclusion of bromine and an acid. An essential aspect of the BZ reaction is its so-called "excitability" — under the influence of stimuli, patterns develop in what would otherwise be a perfectly quiescent medium. Some clock reactions such as the Briggs–Rauscher reactions and the BZ using the chemical ruthenium bipyridyl as catalyst can be excited into self-organising activity through the influence of light. Boris Belousov first noted, sometime in the 1950s, that in a mix of potassium bromate, cerium(IV) sulfate, propanedioic acid (another name for malonic acid) and citric acid in dilute sulfuric acid, the ratio of concentration of the cerium(IV) and cerium(III) ions oscillated, causing the colour of the solution to oscillate between a yellow solution and a colorless solution. This is due to the cerium(IV) ions being reduced by propanedioic acid to cerium(III) ions, which are then oxidized back to cerium(IV) ions by bromate(V) ions. Briggs–Rauscher reaction The Briggs–Rauscher oscillating reaction is one of a small number of known oscillating chemical reactions. It is especially well suited for demonstration purposes because of its visually striking color changes: the freshly prepared colorless solution slowly turns an amber color, suddenly changing to a very dark blue. This slowly fades to colorless and the process repeats, about ten times in the most popular formulation. Bray–Liebhafsky reaction The Bray–Liebhafsky reaction is a chemical clock first described by W. C. Bray in 1921 with the oxidation of iodine to iodate: 5 H2O2 + I2 → 2 + 2 H+ + 4 H2O and the reduction of iodate back to iodine: 5 H2O2 + 2 + 2 H+ → I2 + 5 O2 + 6 H2O See also Catalytic oscillator Mercury beating heart Blue bottle experiment Clock reactions References External links Video of BZ reaction History of oscillating reactions Non-equilibrium thermodynamics Chemistry classroom experiments Chemical reactions Clock reactions